Electric bending machines have been employed in the past to make on-site bends in conduit and pipe for installation in buildings and in which electrical wire or cable are routed to provide electrical service throughout the building. Oftentimes there is a need to effect substantially duplicate bends successively in several conduits or pipes for installation in the building.
A particular electric bending machine used by prior art workers bends the the conduit or pipe about a rotatable shoe while the conduit or pipe is supported by a support roller mechanism. The bending shoe is rotated by an electric motor of permanent-magnet field D.C. type through a reduction gear mechanism. A pipe length is held on the bending shoe by a lug on the shoe and is guided over the support roller assembly as the bending shoe is rotated clockwise. Rotation of the bending shoe is continued until a pointer or other reference marker on the bending shoe moves relative to a bending degree scale on the frame of the machine to the desired degree bend selected; e.g. until the pointer on the shoe registers with the 60.degree. mark on the bending degree scale. The conduit or pipe is removed after bending by rotating the bending shoe in the opposite direction.
In attempting to make duplicate bends in several conduits or pipes, the operator of the machine would place a new length of conduit or pipe in the machine and rotate the bending shoe until the shoe pointer registered with the desired degree bend number on the scale. Typically, the operator would jog the motor to slowly approach the desired degree bend number on the scale. However, due to the inability of mechanical relays in the control circuit to repeat exactly and due to inherent operator error and variation in registering the pointer and scale from one length of conduit or pipe to the next, this procedure is fraught with error so that substantially duplicate bends in several lengths of conduit or pipe are difficult to obtain. Also, this procedure is time consuming on-site as a result of the need to slowly jog the motor of the bending machine to obtain the desired degree bend as accurately as possible.